PCD face seal for earth-boring bit

TECHNICAL FIELD

This invention relates in general to earth-boring bits of the roller cutter variety. More particularly, the invention relates to a seal assembly for sealing lubricant within the bit and excluding drilling environment without the bit, the seal assembly having a polycrystalline diamond (PCD) face.

BACKGROUND ART

One of the most successful seal means used in earth-boring bits of the type having rotatable cutters is the O-ring seal disclosed in commonly assigned U.S. Pat. No. 3,397,928, to Galle. The o-ring seal successfully confines lubricant to the bearing area while excluding detritus for long periods of time before failure.

A more recent seal development is the rigid or metal face seal. In the rigid face seal type, the seal interface is between one or two rigid, usually steel, seal rings. One or two elastomer o-rings serve to energize or urge the seal faces of the rigid ring or rings in contact with each other. The rigid face seal has proved to be as successful as the o-ring seal and provides improved durability in high rotational speed applications.

However, because the seal faces of rigid face seals are in constant contact and slide relative to each other, the dominant mode of failure of the seals is wear. Eventually because of the wear, the seal face geometry changes such that the ability of the seal to maintain sealing effectiveness is lost. This leads to eventual seal failure and ultimately results in bit failure. In an effort to minimize seal wear, rigid face seal rings of prior-art seals are constructed of metal alloys such as 440C stainless steel or cobalt base alloys such as Stellite. Use of these materials for the rigid face seals has resulted in significantly increased bit life, but additional improvement in the seal durability is desirable to extend the life in the most severe applications.

Super-hard materials such as natural and synthetic diamond materials have been used on cutting elements for drill bits for some time. It is also known to utilize polycrystalline diamond (PCD) on cutting elements on drill bits of both the fixed cutter and rolling cone type. Also, PCD is used for thrust bearings for downhole drilling motors. The individual PCD disks are spaced in a circular array around the face of a shaft. The PCD diamond material is usually formed in high temperature and high pressure conditions (“HTHP”) in which the super-hard material is thermodynamically stable. This technique is conventional and known by those skilled in the art. In the most common process, diamond powder is placed in a refractory vessel. A sintered tungsten carbide disk is placed on the diamond powder. The contents of the vessel are then subjected to high pressure and temperature.

Silicon bonded PCD disks are also available, such as described in U.S. Pat. No. 4,793,828. A silicon bonded PCD disk has a mass of diamond particles present in an amount of 80 to 90 percent by volume and a second phase present in an amount of 10-20 percent by volume. The mass of diamond particles contains substantial diamond-to-diamond bonding to form a coherent, skeletal mass. The second phase consists essentially of silicon, the silicon being in the form of silicon and/or silicon carbide.

SUMMARY OF INVENTION

In this invention, the seal assembly is of a rigid face seal type. In one embodiment, at least one of the rigid seal rings has a polycrystalline diamond layer located thereon. The PCD layer is formed on a carbide substrate as a disk in the HTHP process. This results in a fairly thick diamond face having an average thickness in the range from about 0.5 to 5 mm sintered on a carbide backing. A circular central portion of the disk is then cut out, leaving a part in the shape of a washer. The washer may be subsequently shaped to form at least one of the face seals or bonded by a suitable means to a substrate to form at least one of the face seals.

In another embodiment, preferably the binder for the PCD element is silicon without a carbide backing. After the disk is formed, a laser is employed to cut out the central portion. The layer is then secured to a metal body of the ring by brazing or an adhesive such as epoxy. The metal of the ring is preferably a hardened metal, such as steel, but it may also be a carbide. Preferably the opposite or mating face has a PCD face formed in the same manner by an HTHP process. Additionally, one or both of the faces may contain surface features to enhance lubrication of the seal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of one leg of an earth-boring bit having a seal assembly in accordance with this invention.

FIG. 2 is an enlarged sectional view of the seal assembly of FIG. <b>1</b>.

FIG. 3 is a further enlarged view of the mating faces of the seal assembly of FIG. 2, with diamond layers shown exaggerated in thickness.

FIG. 4 is a plan view of one of the rigid seal rings of seal assembly of FIG. <b>2</b>.

FIG. 5 is a plan view of an alternate embodiment of a rigid seal ring for use with the earth-boring bit of FIG. <b>1</b>.

FIG. 6 is a partial plan view of another alternate embodiment of a rigid seal ring for use with the earth-boring bit of FIG. <b>1</b>.

FIG. 7 is a partial plan view of the seal ring of FIG. 6, taken along the line <b>7</b>—<b>7</b> of FIG. <b>6</b>.

FIG. 8 is a partial plan view of another embodiment of a rigid seal ring for use with the earth-boring bit of FIG. <b>1</b>.

FIG. 9 is a sectional view of the seal ring of FIG. 8, taken along the line <b>9</b>—<b>9</b> of FIG. <b>8</b>.

FIG. 10 is a partial plan view of another embodiment of a rigid seal ring for the earth-boring bit of FIG. <b>1</b>.

FIG. 11 is a sectional view of the seal ring of FIG. 10, taken along the line <b>11</b>—<b>11</b> of FIG. <b>10</b>.

FIG. 12 is a plan view of another embodiment of a rigid seal ring for the earth boring bit of FIG. <b>1</b>.

FIG. 13 is a sectional view of the seal ring of FIG. 12, taken along the line <b>12</b>—<b>12</b> of FIG. <b>12</b>.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, bit <b>11</b> has a body <b>13</b>. Body <b>13</b> has a leg with a depending bearing pin <b>15</b> extending downward and inward. Bit <b>11</b> of the embodiment shown will have as many as three bearing pins <b>15</b>, but only one is shown. A cone <b>16</b> is rotatably mounted to each bearing pin <b>15</b>. Cone <b>16</b> has a plurality of external teeth that may be integrally formed with the body of cone <b>16</b>, or formed of tungsten carbide and pressed into holes, as shown.

The bearing spaces between bearing pin <b>15</b> and cone <b>16</b> are filled with a lubricant <b>18</b> (FIG. <b>2</b>). A lubricant compensator <b>17</b> equalizes pressure on the exterior of bit <b>11</b> with the pressure of lubricant <b>18</b> contained in the bearing spaces. A seal assembly <b>19</b> located near the base of bearing pin <b>15</b> seals lubricant <b>18</b> within the bearing spaces.

Referring to FIG. 2, in the preferred embodiment, seal assembly <b>19</b> includes a rigid ring <b>21</b> surrounding bearing pin <b>15</b> near the base of bearing pin <b>15</b>. Rigid ring <b>21</b> is urged into sliding contact with an annular insert <b>23</b>, which is a ring or sleeve shrink-fit into the cavity of cone <b>16</b>. Insert <b>23</b> rotates in unison with cone <b>16</b>, while rigid ring <b>21</b> remains stationary with bearing pin <b>15</b>. An energizing elastomer <b>25</b> is deformed between an inner diameter surface <b>27</b> of rigid ring <b>21</b> and seal cavity <b>29</b>. Energizing elastomer <b>25</b> exerts a force on rigid ring <b>21</b> against insert <b>23</b>. Energizing elastomer <b>25</b> also seals lubricant <b>18</b> located within the bearing spaces. In this embodiment, an excluder elastomer <b>31</b> is also utilized. Excluder elastomer <b>31</b> is deformed between a portion of seal cavity <b>29</b> in bearing pin <b>15</b> and both energizing elastomer <b>25</b> and an end of rigid seal ring <b>21</b>. Excluder elastomer <b>31</b> serves to prevent the entry of debris into contact with energizing elastomer <b>25</b>.

Referring to FIG. 3, preferably both rigid ring <b>21</b> and insert <b>23</b> have a PCD face <b>33</b>, <b>35</b> formed thereon. In the preferred embodiment, the bodies of rigid ring <b>21</b> and insert <b>23</b> are of a hardened metal, such as steel, selected from the group consisting of iron, cobalt and alloys thereof. Referring to FIG. 4, rigid ring <b>21</b> is annular, having an inner diameter <b>37</b> that extends around bearing pin <b>15</b> (FIG. 1) and an outer diameter <b>39</b>. Insert <b>23</b> also has an inner diameter and an outer diameter and is shrink fit in cone <b>16</b> (FIG. <b>2</b>). In this embodiment, faces <b>33</b>, <b>35</b> are smooth and flat and parallel to each other from the inner diameter <b>37</b> to the outer diameter <b>39</b>. Face <b>35</b> is bonded to a metal carbide body <b>36</b> that is mounted in a recess in insert <b>23</b>.

In the preferred embodiment PCD faces <b>33</b>, <b>35</b> are formed as circular disks using a metal binder such as cobalt, nickel, or alloys thereof. In this technique, rigid ring <b>21</b> and body <b>36</b> of insert <b>23</b> are formed of carbide, such as tungsten carbide. A conventional HTHP process for forming PCD diamond material is used. A diamond powder is placed within a refractory container of the desired exterior cylindrical shape. A pre-sintered cemented carbide disk, such as tungsten carbide, is then placed on the diamond powder within the container. Next, the container is surrounded by pressure transmitting material, which is generally salt, boron nitride, graphite or a similar material. This assembly is then loaded into a high pressure and temperature cell. The cell is compressed until the desired pressure is reached and then heat is supplied, normal via a graphite-tube electric resistance heater. Temperatures in excess of 1350° C. and pressures in excess of 50 kilobars are common. At these conditions, the binder metal is molten and acts as a reactive liquid phase to enhance sintering of the diamond material. After a few minutes, the conditions are reduced to room temperature and pressure. The carbide disk with the diamond face is then broken out of the container. Two carbide disks are required, one for rigid ring <b>21</b> and the other for insert <b>23</b>.

Using a conventional electrical discharge machining (EDM) process, a technician then cuts a circular portion out of the center of one of the disks, through the diamond face and tungsten carbide body, to create the annular configuration of seal ring <b>21</b>. The technician repeats the process for insert <b>23</b>. PCD face <b>35</b>, backed with carbide body <b>36</b>, is then brazed or otherwise secured to the remaining portion of insert <b>23</b>, which is of a hardened metal such as steel. The body of seal ring <b>21</b> will preferably be entirely carbide in this embodiment.

In operation, cone <b>16</b> rotates about bearing pin <b>15</b> while bit body <b>11</b> is rotated. Rigid ring <b>21</b> will remain stationary with bearing pin <b>15</b>. Lubricant contained in the bearing spaces is sealed by the dynamic interface between faces <b>33</b>, <b>35</b>. Elastomer energizer <b>25</b> and excluder elastomer <b>31</b> remain stationary with bit body <b>11</b>.

In an alternate embodiment, rather than cobalt or nickel, silicon is used as a binder. PCD components using silicon as a binder are commercially available from DeBeers, Johannesburg, South Africa, under the trademark Syndax. The disks are formed to a thickness of about 0.5 to 2.0 millimeter, with the outer diameter preferably being the same as outer diameters of faces <b>33</b>, <b>35</b>. The silicon base PCD disk does not have a carbide backing, rather it is a free standing disk. A laser is employed to cut circular holes in the disks, forming the inner diameters of faces <b>33</b>, <b>35</b>. Then face <b>33</b> is bonded to rigid backing ring <b>21</b> and face <b>35</b> is bonded to insert <b>23</b>. The bonding may be by brazing or adhesive. The method of attaching should be below the lowest transformation temperature of the material of rigid ring <b>21</b> and insert <b>23</b> so as to not degrade its mechanical properties. The lowest transformation temperatures of iron and cobalt-based alloys, such as 440C stainless steel, is about 730 degrees C. The silicon bonded PCD seal ring may be more difficult to manufacture than the cobalt bonded PCD described above, but the wear characteristics in a sliding tribological couple are better than cobalt bonded PCD.

FIGS. 5-13 illustrate alternate embodiments of the configuration of diamond face <b>33</b>. These alternate embodiments could be utilized for either or both of the faces <b>33</b>, <b>35</b>, regardless of whether PCD faces <b>33</b>, <b>35</b> are formed with silicon as a binder or cobalt as a binder. In the embodiment of FIG. 5, generally rectangular shallow pockets <b>41</b> are formed circumferentially around face <b>133</b>. Each recess <b>41</b> is spaced circumferentially from other recesses and also spaced inward from outer diameter <b>139</b> and outward from inner diameter <b>137</b>. Recesses <b>41</b> serve to retain lubricant.

In FIGS. 6 and 7, recesses <b>43</b> are small circular depressions formed in face <b>233</b> attached to rigid ring <b>221</b>. A number of recesses <b>43</b> are spaced between inner diameter <b>237</b> and outer diameter <b>239</b> of face <b>233</b>. Also, a number of recesses <b>43</b> are spaced around the circumference of face <b>233</b>.

In the embodiment of FIGS. 8 and 9, a plurality of grooves <b>45</b> are formed in face <b>333</b> of rigid ring <b>321</b>. Each groove <b>45</b> extends from the inner diameter <b>337</b> to a land <b>46</b> of specified width at the perimeter <b>339</b> of the seal face. Land <b>46</b> is a smooth flat surface that extends to the outer diameter <b>339</b>. Each groove <b>45</b> intersects other grooves <b>45</b>, forming a diamond cross-hatched pattern.

In the embodiment of FIGS. 10 and 11, face <b>433</b> of rigid ring <b>421</b> has plurality of parallel curved grooves <b>47</b>. Each groove <b>47</b> extends from inner diameter <b>437</b> to a land <b>48</b> of selected width. Land <b>48</b> is a smooth flat surface that extends to the outer diameter <b>439</b>. Grooves <b>47</b> do not intersect each other in the embodiment of FIGS. 10 and 11.

The lubricant pockets, such as shown in FIGS. 5-11, may then be formed by a variety of techniques. In one technique, a laser is used at low power to remove portions of the binder material from the diamond faces <b>33</b>, <b>35</b>. Alternately, a chemical treatment maybe employed. The depths of the pockets are only a few microns.

In the embodiment of FIGS. 12 and 13, seal ring <b>521</b> has an inner diameter <b>537</b> and an outer diameter <b>539</b>. A land <b>49</b> that is flat, normal to an axis of seal face <b>533</b>, and parallel to the surface against which it seals extends inward from the outer diameter <b>539</b> a specified distance. A conical or tapered lubrication surface <b>51</b> of greater width than land <b>49</b> extends inward from land <b>49</b> to inner diameter <b>537</b>. Tapered surface <b>51</b> is located at an angle relative to land <b>49</b> and is not in rotating sealing engagement with a mating surface. The mating surface for seal face <b>533</b> will be flat from its inner diameter to its outer diameter, such as illustrated by seal face <b>35</b> of FIG. <b>2</b>. The width of the mating surface may be approximately the same as the width of seal ring <b>521</b> from its inner diameter <b>537</b> to its outer diameter <b>539</b>, thus only an outer portion of the mating surface will be in rotating engagement with land <b>49</b>. Tapered surface <b>51</b> is located on the lubricant side of the seal ring <b>521</b> when installed to define a space between seal face <b>533</b> and the mating surface to feed lubricant to land <b>49</b>. Land <b>49</b> will enlarge in width as it wears in service.

The invention has significant advantages, providing increased wear resistance, lower coefficients of sliding friction and a lower operating temperature over prior art hardened steel faces. These factors combine to provide a longer lasting seal assembly and, thus, a longer lasting bit.

While the invention has been described in only a few of its forms, it should be apparent to those skilled in the art that it is not so limited, but susceptible to various changes without departing from the scope of the invention. For example, although FIG. 2 shows a single rigid seal ring supported by elastomers and engaging a rigid seal ring fixed to the cone, both rigid seal rings could be supported by elastomers.